10 Bizarre and Fascinating Animal Brains
The human brain is truly astonishing, with more than 100,000 neurons packed into segments the size of a single grain of sand. While our intelligence is undeniable, we are not the only creatures with brains cleverly adapted for survival. From ultra-smart elephants to the small-eared donkey fish (no, really), the weird and wonderful variety of brains found in nature provide an incredible illustration of evolution in action. Let’s take a whistle-stop tour of some of the strangest.
Related: 10 Recently Discovered Awesome Animal Skills
10 Octopus
Being an octopus comes with a unique challenge: how to control all eight of your arms. Fortunately for the octopus, its nervous system allows each arm to work semi-independently from the rest of its body. Unlike humans, octopuses do not have a centralized nervous system, although they do have a main brain between their eyes. More than 60% of the animal’s neurons are located in the arms, with each limb containing as many as 40 million neurons. These neurons act as a ‘mini brain’, allowing each tentacle to process sensory information and determine its own movements.
Therefore, octopuses actually have nine brains, which makes activities such as foraging for food much easier. The central brain acts as a control center, where decisions affecting the animal’s survival are made, while less important decisions are left to individual arms. Fascinatingly, experiments show that octopus arms continue to process and respond to data after being severed, demonstrating the autonomy of the creature’s mini-brain. In 2001, scientists discovered that severed limbs perform the same movements in response to stimuli as arms attached to a living octopus.[1]
9 Spiders
Spinning complex webs takes a lot of brainpower, and it turns out that many spiders simply have huge brains compared to their bodies. Researchers from the Smithsonian Tropical Research Institute set out to find out how the smallest spiders handle this complex behavior. They found that smaller species have proportionately larger brains, and that the smallest species devote up to 80% of their bodies to housing their central nervous systems.
In fact, some small arachnids are so smart that their brains bulge into their limbs and fill up to a quarter of their legs. The babies of this species even have swollen, bulging bodies to house their relatively enormous brains.[2]
8 Cockroaches
You’ve probably heard the hypothesis that cockroaches can withstand nuclear war. Well, these hardy critters can survive decapitation too – at least for a while. Remove the head from a human, and rapid blood loss and the disconnection of the body from the brain ensures almost instantaneous death.
The cockroach has no such problems. The circulatory system maintains a much lower blood pressure than that of humans, so there is no catastrophic blood loss if you remove the head. In addition, clumps of nerve tissue in each part of the body allow the body to continue certain basic functions, such as movement. They can also breathe through small holes called spiracles, which are located throughout the body. Even the heads can survive for a while if you keep them in the refrigerator with a steady supply of nutrients.
All of this begs the question: why bother experimenting with decapitated cockroaches at all? As disgusting as they may be, these grim experiments help us learn how neurons function in other species. Research also suggests that cockroach brains could contain new antibiotics, which could provide an additional tool to help fight infections like MRSA.[3]
7 Sea squirts
Although you wouldn’t guess it from looking at them, the soft-bodied sea squirts are distantly related to humans and belong to the phylum Chordata, a group that includes vertebrates like humans. These humble sea creatures start life with two primitive brains, a spinal cord and neurons to control movements. They then attach permanently to the ocean floor or other stationary underwater object. Because they no longer need the brain responsible for movement, their body reabsorbs one of their two brains and their nerve pathways.
How a sea squirt degenerates its nervous system has surprising consequences for humans. Research shows that the genes that cause neurodegeneration in sea squirts are similar to the genes that cause neurodegeneration in Alzheimer’s disease and several other brain disorders. Studying brain absorption in sea squirts could help scientists understand how conditions like Alzheimer’s disease develop in humans.[4]
6 Giant squid
Giant squids have a beak at the front of their heads, which means their food must pass through the head to reach their digestive system. This interesting digestive arrangement leads to some pretty unusual brain anatomy. To accommodate the esophagus, the giant squid has a donut-shaped brain, which allows the esophagus to pass through the hole in the center. Therefore, everything the creature eats passes through the center of its brain.
As you might imagine, swallowing large chunks of food can damage the squid’s brain as the chunks travel through the esophagus. Fortunately for the squid, it has formidable equipment designed to break down meals into manageable pieces, despite not having teeth in the traditional sense. First, the creature uses its beak to tear apart its food. It also has a radula, a tongue-like structure covered with rows of small teeth. The radula grinds food into small particles to protect the brain and continually grows back to replace worn teeth.[5]
5 Leeches
It is commonly believed that leeches have 32 brains, but this is not entirely true. Instead, these blood-sucking critters have multiple ganglia, which are clusters of nerves that carry signals throughout the nervous system and form the leech’s nerve cord. The leech has two main ‘brains’ at the head and tail, with 21 nerve clusters in the center of the body that act as mini-brains. So that’s a total of 23 ‘brains’ – not the 32 that are often touted.
Scientists have discovered that leeches don’t need all of their brains to perform certain functions by – you guessed it – cutting off their heads. Leeches are good swimmers at the best of times, propelling themselves through the water to find prey. Removing the ganglion at the top of a leech’s ‘main brain’ does not stop it from swimming. Researchers even found that leeches missing their first ganglion swim better than intact leeches.[6]
4 Manta rays
Manta rays have truly colossal brains and the highest brain-to-body ratio of any cartilaginous fish. These big brains result in some impressive smarts. A 2016 study found that manta rays recognize themselves in a mirror, a sign of advanced intelligence found only in a few non-human species. When the beams showed their own reflections, they exhibited unusual, repetitive behavior, demonstrating a degree of self-awareness.
However, possessing a super-smart brain comes with challenges for cold-blooded species. Manta rays often dive deeper than 300 meters below sea level, exposing their bodies to temperatures well below their ideal thermal range. A fascinating structure called the retia mirabilia acts as a built-in heat exchanger, allowing the ray to keep its brain warm and function well in cold conditions. The structure wraps around the creature’s brain and contains a network of veins and arteries. It is thought that basking in warm water before embarking on a deep dive warms the blood in the arteries, transferring heat to the veins through the retia mirabilia.[7]
3 Woodpeckers
Hitting your head repeatedly against a tree is a surefire recipe for a concussion… unless you’re a woodpecker. Scientists have long speculated about how these comical birds can peck hard surfaces up to 12,000 times a day without suffering brain damage. Until recently, it was thought that a spongy part of the skull behind the bird’s beak could act as a crash helmet and absorb blows. While the woodpecker’s tongue extends behind the skull, from the nostrils to the beak, some have even suspected that it holds the brain in place like a seatbelt.
However, none of these theories are convincing, because any form of dampening would prevent the woodpecker from forcefully pecking, which it likes to do. Finally, it seems science has the answer. In 2022, a team of scientists analyzed videos of pecking woodpeckers and found that there is no shock absorption involved.
Instead, the size and shape of the woodpecker’s brain prevents dangerous intracranial pressure. In addition, woodpeckers have minimal space for cerebrospinal fluid, which restricts the brain’s movement within the skull, or “brain sloshing.” According to the researchers’ calculations, a woodpecker could peck twice as fast as normal before risking brain damage.[8]
2 Bony-eared donkey fish
Poor donkey fish with bony ears. Not only does this deep-sea creature have one of the most unfortunate names of all animals, but it is also thought to have perhaps the smallest brain-to-body ratio of any vertebrate. Although the donkey fish has a distinctively bulbous head, relatively little of its enormous skull contains a true brain.
What the donkey fish lacks in brains with its bony ears, it makes up for with its hearing ability. Its skull contains large otoliths, or ‘ear stones’, which allow it to hear low-frequency sounds. The brain itself exhibits several adaptations to help the gentoo fish thrive in its environment, such as a large cerebellum. These features can give the creature a keen sense of its own movement and the position of nearby objects. Maybe small brains aren’t so bad for the donkey fish, because an improved sensory system could be a big advantage in a dark, deep ocean environment.[9]
1 Elephant
When it comes to brain size, bigger is not always better. Elephants are known for their intelligence and possess impressive memory, social and problem-solving skills. However, their intelligence does not match that of humans – at least by our own standards. Elephant brains weigh three times more than human brains and contain 257 billion neurons compared to our modest 86 billion, so why can’t they outsmart us?
According to a 2014 study, it’s not just the total number of neurons that determines an animal’s cognitive abilities. Elephants may have more neurons than us, but the vast majority are in the cerebellum (the part of the brain that controls muscle activity). However, humans have about three times as many neurons in our cerebral cortex. Our highly developed cerebral cortex allows us to develop higher-level thinking skills, such as learning, reasoning and language production.[10]